The invention relates to golf club shaft made from fibre-reinforced plastic, with a portion for the attachment of a club head provided in its lower end region and a portion for the attachment of a grip provided on its upper end region, the shaft forming a hollow profile, whose cross-section is not constant over the shaft length and has a symmetrical shaping to a median plane passing through the longitudinal axis of the shaft in the drive direction and with a flex point in the area between the two portions used for attaching a club head or a grip.
The use characteristics of a golf club are inter alia decisively influenced by the material of the club shaft and the design of the latter.
It is known to construct golf clubs with a solid wooden shaft. Such golf clubs were widely used in earlier times. However, of late, increasing use is being made of golf clubs, in which the shaft is constituted by a stainless steel tube or a fibre-reinforced tube having a circular cross-section and which at least over part of the shaft length between the grip and the club head tapers in the direction of the latter. The taper can take place conically or stepwise by fitting into one another tubular portions of decreasing cross-section and it is even possible to combine together tubular portions made from different materials (metal, fibre-reinforced plastic) (European patent 258 233).
It is fundamentally desirable in a golf club for its weight to be as low as possible, which can be achieved in the case of shafts made from fibre-reinforced plastic. However, it is simultaneously desirable for there to be a clearly defined resilience (rigidity) of the club shaft when driving.
Hitherto known golf club shafts made from fibre-reinforced plastic are constituted by a circular tube (e.g. U.S. Pat. No. 3,998,458 and German patent 23 48 011) and have a relatively great flexibility, which impairs the precision of the drive in both the vertical and horizontal direction and it is scarcely possible to accurately control the trajectory of the ball. On driving the shaft initially bends in a first portion of the driving, movement counter to the driving direction, so that the club head trails somewhat in the latter. This rearward bending of the shaft is cancelled out again in a second portion of the driving movement and then in a third portion of the latter, which starts directly before ball contact, the shaft bends forwards in the direction of movement. If ball contact (tee-shot) takes place in this phase, there are changes to the ball take-off angle predetermined by the club head inclination and which consequently changes in an uncontrollable manner. The take-off speed of the driven ball also suffers as a result of the energy loss caused by the shaft deformation. The point along the shaft where the maximum shaft deflection occurs on driving (relative to the connecting line between the start and finish of the shaft) is known as the flex point.
As the nodal point of vibration of the vibrations on the club occuring on driving is directly below the hands or the handle, in the known, fibre-reinforced plastic club shafts, considerable jolting occurs on the forearm of the golfer.
A primary object of the invention is therefore to so improve a fibre-reinforced plastic hollow shaft for a golf club in such a way that for the same club loading when driving there are reduced deformations of the club shaft compared with conventional fibre-reinforced plastic club shafts and it is consequently possible to more accurately determine the ball take-off angle on driving, while obtaining an increased ball take-off speed.